This invention relates generally to electro-optic structures and devices and to a method for their fabrication, and more specifically to an improved electro-optic structure and to a method for monolithically integrating the electro-optic structure with silicon devices and circuits.
In general, communication systems transmit information from one place to another. Information is often carried by an electromagnetic carrier wave whose frequency can vary from a few megahertz (MHz) to several hundred terahertz (THz).
Typically, optical communication systems use high carrier frequencies (e.g.,100 THz) in the visible or near-infrared region of the electromagnetic spectrum.
Waveguides are used to control the direction of waves such as lightwaves and other electromagnetic waves. In the simplest form, a waveguide includes a core surrounded at least partially by a cladding whose refractive index is lower than that of the core. The wave travels through the core reflecting off of the cladding. If the cladding has a higher refractive index than the core, the wave will simply be absorbed into the cladding and will not travel through the core.
Strontium barium niobate (SBN) is strongly photorefractive material and in recent years has received a great deal of attention due to its potential applications in electro-optics, holographic storage, spatial light modulators, pyroelectric detectors, surface acoustic wave devices and beam steering. SBN waveguides show a high compatibility with integrated optical systems and other miniaturized devices.
The vast majority of semiconductor discrete devices and integrated circuits are fabricated from silicon, at least in part because of the availability of inexpensive, high quality monocrystalline silicon substrates.
The combination of the useful properties of SBN with semiconductor circuits is also desirable. If SBN waveguiding films could be fabricated on silicon substrates, this would help to bridge the gap between integrated optics and microelectronics. If a waveguiding film of high quality monocrystalline material could be realized on a bulk wafer such as a silicon wafer, an integrated device structure could be achieved that took advantage of the best properties of both the silicon and the waveguiding material. In addition, the combination could lead to new electro-optic and microelectronic devices, improve existing devices and reduce their fabrication costs.
Various attempts have been proposed to integrate SBN films on bulk substrates.
For example, the combination of SBN film on a MgO (magnesium oxide) substrate showed some favor due to the lower refractive index of MgO which resulted in a refractive index difference of 0.5. However, silicon substrates are much more desirable for integration purposes.
Another attempt proposed by X L Guo et al., xe2x80x9cPulsed Laser Deposition of SrxBa1xe2x88x92xNb2O6/MgO Bilayered Films on Si Wafer in Waveguide Form,xe2x80x9d J Phys. D: Appl. Phys. 29, 1996, pp. 1632-35, teaches a method of fabrication of SBN/MgO bilayered films on p-type silicon wafers. The bilayered film shows a polycrystalline growth of SBN films and highly textured growth of MgO buffer layers. However, as X L Guo et al. admits, the resulting polycrystalline structure is not as desirable as a monocrystalline structure and therefore, further efforts shall be made to improve the crystallinity of the SBN film.
Accordingly, a need exists for an electro-optic structure having high quality monocrystalline characteristics. In particular, a need exists for an electro-optic structure which is monolithically integrated with silicon-based circuitry wherein the structure is of high quality monocrystalline material.